The present invention relates to a chemical mechanical polishing slurry and a chemical mechanical polishing apparatus and method, and more particularly to a chemical mechanical polishing slurry and a chemical mechanical polishing apparatus and method, in which defects, such as scratches, are reduced while maintaining a high polishing rate of a target film to be polished through a chemical mechanical polishing process.
A chemical mechanical polishing process (hereinafter, referred to as a “CMP” process) is performed by supplying a slurry to a polishing pad of a chemical mechanical polishing apparatus (hereinafter, referred to as a “CMP” apparatus) and rotating a target film on a semiconductor wafer on the polishing pad. The target film is polished by a chemical reaction between the target film and the slurry and mechanical friction between an abrasive (particles of the abrasive) in the slurry and the target film.
Generally, a slurry including either a silica(SiO2)-based abrasive or a ceria(CeO2)-based abrasive has been used in the CMP process.
A slurry including a silica-based abrasive has an aqueous solution state. For example, the slurry has an acidity of pH 9 or more. Particles of the abrasive are relatively large in size. The slurry has a relatively large weight and high viscosity due to a high molecular weight of silica. Thus, the particles of the silica-based abrasive cohere, and the slurry easily solidifies on the polishing pad.
The above solidified slurry is not easily removed, and generates defects, such as scratches on the target film, after the polishing pad has been used and the CMP process has been repeatedly performed, thereby highly influencing the reliability and the yield of the CMP process. For reference, FIGS. 1A and 1B are SEM photographs illustrating scratches on a target film, after the CMP process is performed.
When a ceria-based abrasive is used, the polishing rate of a target film to be polished, in an initial step in which there are stepped portions on the target film, is lowered due to a loading effect. The lowering of the polishing rate of the target film causes the stepped portions on the target film to be not properly removed, thereby reducing the productivity of the CMP process.
In order to solve the above drawbacks, a method for performing a CMP process has been proposed that includes a first polishing step using a slurry including a silica-based abrasive and a second polishing step using a slurry including a ceria-based abrasive. However, the slurry including the silica-based abrasive also solidifies on a polishing pad due to the cohesion of particles of the silica-based abrasive, and generates defects, such as scratches on the target film, thereby lowering the reliability and the yield of the CMP process.